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Atari 1200xl Black Screen

We have an Atari 1200xl computer which is in perfect physical condition. History of this machine is not known. When powered on, the power LED lights, the screen flashes red for a brief moment, then goes to pure black. There are two soft "pop" sounds from the tv speaker during the start up process as well. Pressing the reset button causes the two pops to be heard, but the screen remains black. We have tried both the RF and composite outputs with the same result. We have also tried 2 different power supplies, and swapped the ANTIC chip but the problem persists. I have removed and reseated all socketed chips, and moved the RAM chips around but there is still no change. Any assistance is appreciated. Thanks!

Yes, the tv works with multiple other vintage systems using both RF and composite in. The only cart I have is the BASIC cart, and I have tried it both with and without the cart installed with the exact same result.

So, I fired up a 1200XL to see what happens using the composite jack with neither drives nor cart. You should expect the system to post an ATARI logo on the screen. I guess you have to troubleshoot the motherboard of the computer.

Just swapping around the RAM chips might not be enough. It's very conceivable that more than one RAM chip is bad. Bad RAM will produce symptoms like yours on an 800XL, so I assume the same would be true for the 1200XL. Sometimes bad RAM will be warm to the touch, but not always. I would have had a very hard time repairing my XLs or my C64s without a way to test 4164 RAM chips.

So, I fired up a 1200XL to see what happens using the composite jack with neither drives nor cart. You should expect the system to post an ATARI logo on the screen. I guess you have to troubleshoot the motherboard of the computer.

It's the GE TV monitor / printer interface display. You can have multiple computers attached at a time, switch (box) on the front, plus a printer. Both RF and composite, with variations of audio. The perfect bench display.
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Just wanted to close the loop on this thread, in case that it is helpful to anyone else out there. This issue was resolved by replacing the POKEY chip. I had noticed that the MMU chip was also getting a bit hot when the machine would not start, so we started by swapping that. However, the same symptom of black screen was present. Once POKEY was replaced, everything is now working perfectly.